Reddit reviews Brit-Think, Ameri-Think: A Transatlantic Survival Guide, Revised Edition

Hardest thing was definitely getting the work permit; after that, everything else kind of fell together in a follow-your-nose domino cascade, in which each step kind of points directly to the next. We ended up hiring an immigration consultant in the UK to walk-through the application, which isn't necessary but did speed the process and increased our probability of success.

I guess the most important thing in actually making it happen is: believe it will. It may take a few years. Don't give up. You may bounce off quota limitations a few times. Don't let it faze you, because those get changed every 6mo (along with the rest of the immigration procedure...) Keep your options flexible: while London may be your ultimate goal, there are many routes to get there, some of which could entail starting with a different EU country and pursuing naturalization there (this would take many years, and assumes the UK will still be in the EU once you attain it...) You're young, and have a whole lifetime to achieve such goals. We were in our late 30's when we finally made it. Take your time, do it right.

We're bookish types, and so looked for books that might advise/ease the process. Unfortunately there's not a lot out there on expatriation, but it's worth checking Amazon's "used" listings periodically as prices fluctuate. Probably the two we found most useful were the U.S. Expatriate Handbook (generic expat guide) and Brit-Think, Ameri-Think.

The biggest mistake we made was deciding to import our US car. This was actually done on the advice of some British neighbors in the US, and we still haven't resumed talking to them after that fiasco ;-) If you're living within Greater London (inside the M-25, within 1/2 mile of a Tube station) then you probably shan't need a car at all. If you do decide to get one, note that for your first 12mo in the UK (not your first 12mo owning a car) you can drive on your US license, then you need a full UK license. It can take several months to obtain the UK license (most of my friends took 3+ attempts to pass the rigorous driving test at 1-mo intervals), so start early.

Taxes will be a minor twice-yearly nightmare. You still have to file your US taxes every April 15th, although you shouldn't have to pay much, if anything, due to the Foreign Earned Income Exclusion (read up on it). Your UK taxes will be vastly simpler by comparison, as the employer basically does it all for you. Also, don't forget to mail your FBAR (TDF-90.22) assiduously every year by June 1st (actually due the 30th, but leave time for delivery) — seriously, you can get deeply screwed if you forget that one, and there's no reminder (although it's free and only takes seconds to complete).

You can look for US Expat groups in the UK for company whilst readjusting. You'll not need them long-term, but it can be interesting to hear some local voices on first entry. There are about 60,000 US citizens in the London area, so they should be easy to find in your particular area (we met with the Thames Valley American Women's club a few times, but didn't stay long). Also of course checkout /r/london and similar. And it can be neat to attend St. Paul's annual Thanksgiving service for Americans :-)